This invention relates to a method and apparatus for rolling rails.
In deciding the number and layout of stands for rolling shapes in general, the most economical layout is chosen with the intended product mix, quantity of production and quality control requirements in view. In order to obtain the mechanical properties desired in rails, the rolling apparatus and method must be capable of providing a total elongation (the ratio between the cross-sectional areas of the bloom and product rail) of not lower than 8.0 using continuously cast blooms for rails as specified by the British Standards.
FIG. 1 shows the layout of a typical universal rail rolling mill. At this mill, a bloom BL is rolled into a product rail by a breakdown stand BD, a roughing stand R, a first universal stand U.sub.1, an edger stand E, a second universal stand U.sub.2, a head-wheel stand H, and a base-wheel stand B in that order. FIG. 2 shows the rolls and pass contours of the individual stands. The piece passes over the breakdown stand BD seven times, the rolls thereon forming six passes 1 through 6. The piece passes over the roughing stand R three times, the rolls thereon forming three passes 7 through 9. The last pass 9 in the roughing stand R is vertically symmetrical with respect to the horizontal center line and called the "reforming pass." The shape of the finished rail is symmetrical with respect to the center line of the web. As shown in FIG. 2, all passes formed by the first universal stand U.sub.1 through the base-wheel stand B are symmetrical with respect to the center line of the web. For this reason, it is essential to pass the rail through the reforming pass 9 immediately before rolling in the first universal stand U.sub.1 is implemented.
Reversed rolling is effected three times continuously between the first universal stand U.sub.1 and the edger stand E. Two passes 11 and 12 are formed by the rolls of the edger stand E. The rolling operation between the first universal stand U.sub.1 and the edge stand E is carried out by passing the piece through the passes in the following order; 10-11-11-10-10-12. The cross-section of the piece grows smaller each time it passes through the pass 10 on the universal stand U.sub.1 since both horizontal and vertical rolls thereon are brought closer for every succeeding passage. The shape of the pass 11 conforms to the cross section of the piece that is attained after the first passage through the pass 10 on the universal stand U.sub.1, while the shape of the pass 12 conforms to the cross section of the piece that is attained after the third passage therethrough. The edger stand E has a quick pass replacer QS that brings the pass 11 or 12 into rolling position in conformity with the number of the rolling being conducted in the preceding universal stand U.sub.1.
One continuous rolling operation is implemented between the second universal stand U.sub.2 and the head-wheel stand H. The second universal stand U.sub.2 has a head-side vertical roll 13 which is kept in contact with the side MT of horizontal rolls 14. This arrangement is essential for defining the thickness and height of the rail head. On the head-wheel stand H where pre-finishing rolling is conducted, fine adjustment of the head thickness and base width is achieved by adjusting the position of a head-side vertical roll 15 and horizontal rolls 16. On the base-wheel stand B where finishing rolling is conducted, fine adjustment of the head width, web thickness and base thickness is achieved by adjusting the position of a base-side vertical roll 17 and horizontal rolls 18.
As might be understood from the above description, the universal rail rolling method and apparatus must fulfill the following requirements:
(1) The reforming pass is provided immediately ahead of the universal rolling stand. PA1 (2) The final universal rolling is carried out with the head-side vertical roll kept in contact with the side of the horizontal rolls. PA1 (3) The product rail is finished by applying the universal, head-wheel and base-wheel rolling in that order.
Generally, the ratio between the cross-sectional areas which the piece possesses before and after passing through a single pass is known as "elongation." Table 1 lists approximate values of elongation resulting from the passes peculiar to the universal rolling of rails.
TABLE 1 ______________________________________ Rolling Stand R (Pass 9) U.sub.1 E U.sub.2 (MT) H B ______________________________________ Elongation 1.08 1.25 1.02 1.15 1.03 1.07 ______________________________________
FIGS. 3 and 4 show conventional universal rail rolling mills that are simpler than the one shown in FIG. 1. The mill in FIG. 3 dispenses with the roughing stand R shown in FIG. 1, whereas that in FIG. 4 dispenses with the second universal stand U.sub.2 and head-wheel stand H. With respect to the mill of FIG. 4, it may be said that combining the edger stand E and head-wheel stand H into a rolling stand EH has permitted integrating the universal stands U.sub.1 and U.sub.2 into one universal stand.
The number of passes in the mill shown in FIG. 4 is fewer than that in the mill of FIG. 1 because one pass through each of the second universal stand U.sub.2 and edger stand E are omitted. However, two additional passes are carried out in the breakdown stand BD in order to obtain a greater total elongation. Nevertheless, the number of passes and stands as a whole is not sufficient.
In the mill of FIG. 3, omission of three passes in the roughing stand R is made up for by providing the greatest elongation among the three mills being discussed in the breakdown stand BD. Despite this, however, total elongation is only slightly greater than 8.0. Owing to this insufficient elongation, the mill shown in FIG. 3 does not use a reforming pass.
Because of the poor reforming function, these conventional rolling methods and apparatuses have been unable to roll rails with a high degree of dimensional and shape accuracy without employing a large number of passes.